title: ProQ is an RNA chaperone that controls ProP levels in Escherichia coli.
abstract: Transporter ProP mediates osmolyte accumulation in Escherichia coli cells exposed to high osmolality media. The cytoplasmic ProQ protein amplifies ProP activity by an unknown mechanism. The N- and C-terminal domains of ProQ are predicted to be structurally similar to known RNA chaperone proteins FinO and Hfq from E. coli. Here we demonstrate that ProQ is an RNA chaperone, binding RNA and facilitating both RNA strand exchange and RNA duplexing. Experiments performed with the isolated ProQ domains showed that the FinO-like domain serves as a high-affinity RNA-binding domain, whereas the Hfq-like domain is largely responsible for RNA strand exchange and duplexing. These data suggest that ProQ may regulate ProP production. Transcription of proP proceeds from RpoD- and RpoS-dependent promoters. Lesions at proQ affected ProP levels in an osmolality- and growth phase-dependent manner, decreasing ProP levels when proP was expressed from its own chromosomal promoters or from a heterologous plasmid-based promoter. Small RNA molecules are known to regulate cellular levels of sigma factor RpoS. ProQ did not act by changing RpoS levels since proQ lesions did not influence RpoS-dependent stationary phase thermotolerance and they affected ProP production and activity similarly in bacteria without and with an rpoS defect. Taken together, these results suggest that ProQ does not regulate proP transcription. It may act as an RNA-binding protein to regulate proP translation.
authors.affiliation: Department of Biochemistry, School of Molecular and Systems Medicine, University of Alberta, Edmonton, Alberta, Canada T6G 2H7.
authors.forename: Steven G
authors.initials: SG
authors.lastname: Chaulk
authors.forename: Michelle N
authors.initials: MN
authors.lastname: Smith Frieday
authors.forename: David C
authors.initials: DC
authors.lastname: Arthur
authors.forename: Doreen E
authors.initials: DE
authors.lastname: Culham
authors.forename: Ross A
authors.initials: RA
authors.lastname: Edwards
authors.forename: Patrick
authors.initials: P
authors.lastname: Soo
authors.forename: Laura S
authors.initials: LS
authors.lastname: Frost
authors.forename: Robert A B
authors.initials: RA
authors.lastname: Keates
authors.forename: J N Mark
authors.initials: JN
authors.lastname: Glover
authors.forename: Janet M
authors.initials: JM
authors.lastname: Wood
mesh_terms: D000595:Amino Acid Sequence; D004926:Escherichia coli / Q000235:genetics / Q000378:metabolism*; D029968:Escherichia coli Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D056426:Genetic Loci / Q000235:genetics; D026901:Membrane Transport Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008958:Models, Molecular; D018832:Molecular Chaperones / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D009154:Mutation; D011401:Promoter Regions, Genetic / Q000235:genetics; D017434:Protein Structure, Tertiary; D012329:RNA, Bacterial / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D012330:RNA, Double-Stranded / Q000378:metabolism; D016601:RNA-Binding Proteins; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D014158:Transcription, Genetic
chemical_list: D029968:Escherichia coli Proteins; D026901:Membrane Transport Proteins; D018832:Molecular Chaperones; C079244:ProP protein, E coli; C118132:ProQ protein, E coli; D012329:RNA, Bacterial; D012330:RNA, Double-Stranded; D016601:RNA-Binding Proteins; D027981:Symporters